Water-soluble pyridinium compounds, quaternary ammonium compounds and biguanide compounds are effective cationic bactericides for inhibition of plaque formation, and there have hitherto been made a proposition that these bactericides are blended in toothpaste compositions. When these compounds are mixed with anionic ingredients such as thickening agents or surfactants in toothpaste compositions, they may cause electric reaction to deteriorate their bactericidal activity because of their cationic properties. To prevent such an electric inactivation of bactericidal activity, there is proposed a combination of cationic bactericides and nonionic thickening agents or cationic polymers (see, e.g., JP-A 2-223511, JP-A 3-127718 and U.S. Pat. No. 5,176,901). However, although the bactericidal activity of the cationic bactericides is stabilized in these compositions, the compositions have poor paste-shape retention and poor rheological properties in the sense of use.
To obtain a toothpaste composition having good shape retention, there has been made a proposition that a cationic polymer is blended in the composition. For example, a cationic polymer is combined with silica to cause flocculation between both substances, so that thickening properties are improved to form a gel. However, the gel stability is readily deteriorated with time, such as solid-liquid separation, and silica has silanol groups which can absorb any cationic bactericide and thereby inactivate its bacteriocidal activity.